Aligomeric polyacrylates

ABSTRACT

The present invention relates to a novel class of oligomeric builders for use in detergent compositions. More particularly, the present invention relates to a biodegradable, oligomeric polyacrylate having a molecular weight of greater than about 500 and less than about 10,000, preferably less than about 5000. In the most desirable embodiments at least one end of the oligomer chain is terminated with either a sulfur containing moiety or an hydroxy containing moiety. Preferred cations are alkali metals, ammonium and substituted ammonium.

This is a division of application Ser. No. 461,060, filed Apr. 15, 1974now U.S. Pat. No. 3,922,230 which is a continuation of Ser. No. 169,101,8/4/71, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Non-phosphorus oligomeric biodegradable builders for detergentcompositions.

2. Description of the Prior Art

In recent years the problem of eutrophication, which can be defined as aslow rate, natural process of enrichment of waters with nutrients, suchas phosphorus and nitrogen has received much notoriety. Uncontrolled orpronounced eutrophication has been found to cause increased algal growthand agal scums which not only are unaesthetic, odorous, distasteful andclog filters or treatment plants but also creates disproportionatedemands on the available oxygen in the water. It has been postulatedthat in several bodies of water various human activities havecontributed to acceleration of the process through such factors asinordinate enrichment of natural runoff, ground water and agriculturaldrainage, sewage and waste effluents. It has also been suggested thatthe phosphorus-containing builders present in detergent compositions canbe a contributing factor in eutrophication, and therefore anysubstitutes which do not contain phosphorus may decrease to some extentthe eutrophication problem. Thus, those skilled in the art have expendeda great deal of time and money to solve this problem and find suitablematerials to reduce or replace the existing phosphate builders indetergent compositions. This work is still continuing since most of thebuilders discovered to date have been deemed unsatisfactory for avariety of reasons and are most often less efficient than the existingphosphate builders.

High molecular weight acrylate polymers have been known in the art formany years, finding significant use as molding resins, films and fibers.Particular species of the higher molecular weight acrylate polymers,such as sodium polyacrylates in British Pat. No. 1,090,809 and alphahalogen substituted polyacrylates such as polyalpha chloracrylic acid,polyalpha fluoracrylic acid and copolymers thereof with otherpolymerizable organic compounds, in U.S. Pat. No. 2,327,302 have beensuggested as capable of functioning as detergent assistants. Thesecompounds, however, create as much, if not more, of a problem than theyostensibly solve since at the molecular weight of the polymers believedcontemplated by these patents, the molecules could not be biodegradable.

A large proportion of the sanitary treatment performed in this countryis done aerobically. If the bacteria in the degradation system cannotconsume and degrade a molecule it may pass through the tank and flowinto the surrounding area, ultimately mixing with the surface water andeventually becoming part of the human water supply. It has been foundthat, bacteria either cannot or have extreme difficulty in degradinglong chain polymers and branched polymers of the type disclosed in theabove patents. Since so little is known about the effects of so manychemicals, particularly from a carcinogenic and birth defectsstandpoint, when ingested by human beings, a compound intended for usein a detergent formulation must be biodegradable or it is dropped fromfurther consideration. As such, the compounds of British Pat. No.1,090,809 and of U.S. Pat. No. 2,327,302, as well as other relativelyhigh molecular weight polyacrylates would be deemed unacceptable for usein a detergent formulation.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide novelbiodegradable builder compounds which are free of phosphorus and can beincorporated into detergent compositions.

The compositions of the invention necessarily include both a syntheticbuilder and a water-soluble organic detergent compound; such as theanionic (soap and non-soap), nonionic, zwitterionic and ampholyticdetergent compounds. The chemical nature of these detergent compounds isnot an essential feature of the present invention, snce these are wellknown to those skilled in the detergent art and the literature isreplete with disclosures of such compounds. Typical of such literatureare "Surface Active Agents" by Schwartz and Perry and "Surface ActiveAgents and Detergents" by Schwartz, Perry and Berch, both of which arepublished by Interscience Publishers, Inc., New York, New York, thedisclosures of wich are incorporated herein by reference.

The phosphorus-free builders for the detergent compositions of thepresent invention are the alkali metal, ammonium and substitutedammonium salts of low molecular weight polyacrylic and polyalkylarylicacid. More particularly, the polymers have an average molecular weightof between about 500 to about 10,000 with a preferred range of less thanabout 5000 and a most preferred range of less than about 3000.

DETAILED DESCRIPTION OF THE INVENTION

As discussed above the search for a phosphorus-free detergent buildercomposition has engendered a great deal of effort and expense on thepart of the detergent industry. Basically, the criteria that a newbuilder must meet, aside from being free of phosphorus, are, first, thatwhen incorporated into a detergent formulation, the resultant detergentefficiency of the formulation is equal to or closely approximates thatof a similarly formulated, phosphorus built detergent; and, second, thatthe builder be biodegradable. As to the first requirement, it isaxiomatic that a replacement for an established product must be at leastas good as the established product if it is to gain any consumeracceptance. The second requirement is a result of the large proportionof aerobic sanitary treatment facilities in this country. Anypossibility that a compound will pass through a treatment system, intothe surrounding surface water and become part of the available watersupply without substantialy bacteriological degradation necessitatesrejection of that compound for use in a detergent formulation.

The present invention meets both of these criteria and provides abiodegradable detergent builder which when incorporated into aformulation results in excellent detergent efficiency. As will now bedescribed, the present invention is the discovery that certain acrylatepolymers have unique and excellent detergent building properties. Theparticular acrylate polymers found useful are those having an averagemolecular weight of between about 500 and about 10,000, preferably lessthan 5000 and in the most preferred form, less than about 3000. At theselevels the acrylate is more properly referred to as an "oligomer" ratherthan a "polymer" and will be so referred to hereinafter.

Experimentation with these compounds has shown that the chainterminating moiety plays an important part in both the building abilityof the polyacrylate and in the relative ease of biodegradability.Although any chain terminating or chain transfer agent which willreasonably function with polyacrylate and does not impairbiodegradability of the molecule may be used, such as alkyls,substituted alkyls, hydrogen and the residue from a free radicalinitiator, the preferred embodiments utilize compounds which willterminate at least one end of the chain with a sulfur containing moietyor an hydroxy containing moiety.

Examples of the type of compounds which can terminate a polyacrylatechain with either an hydroxy and/or a sulfur containing group include,but are not limited to, alkanols, preferably having from one to sixcarbon atoms, glycols, glycol esters, glycolic acids and salts thereof,thiols having from one to twenty carbon atoms, thio carboxylic acidshaving at least one carboxylic group and salts, thereof, thio alkanolsand hydroxy substituted thiols. Although the mechanism and reasons arenot completely understood, hydroxy and sulfur containing moietys,particularly sulfur containing moietys at the ends of the oligomericpolyacrylates of the present invention, enables use of lowerconcentrations of the detergent formulation in the wash solution thandoes an otherwise terminated acrylate without any impairment ofdetergent efficiency. In addition, these terminating groups arepreferred because they permit use of lower weight and, therefore, morebiodegradable oligomers than do other end caps to obtain the samerelative building ability in the detergent formulation.

Preferred cations for the acrylate salts are the alkali metals, ammoniumand substituted ammonium such as morpholinium, alkyl ammonium, mono-,di-, and tri-alkanol ammonium and tetra alkyl ammonium. It should beunderstood that the term polyacrylates, as used herein, includes withinthe definition, as an integral part thereof, polyalky-acrylates of fromone to six carbon atoms; these also being considered efficacious asdetergent builders. In this regard, the lower members of the group,i.e., methyl, ethyl and propyl acrylates are the most responsive to theneeds of a detergent formulaton. It should also be understood at thisjuncture that the term polyacrylates refers to acrylate homopolymers,acrylate copolymers and terpolymers, etc. wherein the acrylate moietycomprises at least 45 mole percent of the molecule.

The unique compounds found suitable for the present invention may thusbe summarized by the general formula: ##STR1## wherein n is a series ofwhole number integers such that the average molecular weight is lessthan about 10,000 preferably less than about 5000; R₁ and R₂ aremoieties which do not impair biodegradability of the molecule such as,for example, alkyls, substituted alkyls, hydrogen, the residue from afree radical initiator, alkanols preferably having one to six carbonatoms, glycols, glycol esters, glycolic acids and salts thereof, thiolshaving from one to twenty carbon atoms, thio carboxylic acids having atleast one carboxylic group and salts thereof, thio alkanols and hydroxysubstituted thiols; R₃ is selected from the group consisting of hydrogenand alkyls having from one to six carbon atoms; and, M is selected fromthe group consisting of alkali metals, ammonium and substituted ammoniumcations.

The weight ratio of the builder compounds of the present invention todetergent compound when used in laundering and hand dishwashingcompositions, ranges generally from about 1:20 to about 20:1. When thenovel builders are used in mechanical dishwashing compositions, theratio of builder to detergent compound is from about 10:1 to about 50:1.

Builder compounds of the present invention can be used either as thesole builder or where desired can be used in conjunction with otherbuilders, examples of which include the alkali metal salts ofcarboxymethyloxysuccinic acid and oxydiacetic acid, tetrasodium andtetrapotassium pyrophosphate, pentasodium and pentapotassiumtripolyphosphates, ether polycarboxylates, citrates, starch or cellulosederived polycarboxylates, and the like. Other materials which may bepresent in the detergent compositions of the invention are thoseconventionally present therein. Typical example thereof include soilsuspending agents, hydrotropes, corrosion inhibitors, dyes, perfumes,fillers, abrasives, optical brighteners, enzymes, suds boosters, sudsdepressants, germicides, anti-tarnishing agents, cationic detergents,softeners, chlorine releasing agents, buffers and the like. The balanceof the detergent compositions is water.

The detergent compositions of the present invention may be in any of theusual physical forms for such compositions, such as powders, beads,flakes, bars, tablets, noodles, liquids, pastes, and the like. Thedetergent compositions are prepared and utilized in the conventionalmanner.

When using the detergent compositions of the invention to wash clothes,the wash solutions should have a pH from about 7 to about 12, preferablyfrom about 9 to 11. Therefore, the presence of a buffer in the detergentcomposition is usually desirable. Examples of such buffers are sodiumsilicate, carbonate or bicarbonate.

When the pH value of the wash solution is below about 8.6 some of thesalts of the builder compounds will be present in the acid salt form andsome in the normal salt form.

It should also be noted that when the compounds of the present inventionare employed as the free acids or as partly neutraized salts, thecompounds have utility in metal cleaning compositions under pHconditions of about 2 to about 5.

The following examples demonstrate without limiting the presentinvention preparation of low molecular weight polyacrylates suitable foruse in detergent formulations, demonstrates their efficacy as detergentbuilders and thier biodegradability.

EXAMPLE I

A screw cap flask is charged with 80g. water, 20g. isopropanol, 1.7g of30% hydrogen peroxide and 10g. of glacial acrylic acid. The reactionsolution is then heated at 83° C for 67 hours. After cooling theremaining peroxide is destroyed using Pt foil as a catalyst. Afterevaporation of the solvents the polymeric residue is purified bydissolving in ethanol and precipitating with 2-butanone. The filteredproduct is then dried in a high vacuum drying pistol. A molecular weightdetermination using Vapor Phase Osmometry gives a value of ˜10,270.

EXAMPLE II

The preparaton described for Example I is repeated except that thereacting solution contains 70g. of water, 30g. isopropanol, 2.3g. of 30%hydrogen peroxide and 10g. of glacial acrylic acid. The averagemolecular weight of the oligomer obtained is ˜3000.

EXAMPLE III

The preparation described for Example II is repeated except that 30g. ofehtyl glycolate is used in place of the isopropanol as the chaintransfer agent and the reaction time is 19 hours. The molecular weightof the purified oligomer is ˜2000 as determined by Vapor PhaseOsmometry.

EXAMPLE IV

A solution of 300 ml. of isopropanol containing 10g. of acrylic acid isheated to reflux. Then, 0.75g.-of azo-bis-isobutyronitrile (AIBN) isadded and the resulting solution, refluxed for 1 hour. The reactionmixture is then added to 800 ml of benzene and the resulting solutionconcentrated to 200 ml. The precipitated polymer is separated bycentrifuging and dried in a vacuum oven at 55° C in the presence of P₂O₅ ; the yield is 5.1g. The average molecular weight of the product asdetermined by Vapor Phase Osmometry is ˜1050.

EXAMPLE V

The sodium salts of the above oligomeric polyacrylic acids are preparedby dissolving the oligomer in water and neutralizing with dilute soliumhydroxide to pH = 8.6 The solution is then evaporated to dryness torecover the dry solid sodium salt.

EXAMPLE VI

A solution of acrylic acid, AIBN and n-dodecyl mercaptan in 300ml ofmethanol is refluxed for 2 hours. The reaction mixture is thenconcentrated to about 50 ml by evaporation in vacuo. Benzene, 100 ml, isthen added whereby a lower oily layer is separated. After decanting theupper benzene layer, the lower layer is dissolved in 20 ml of methanoland treated again with benzene to separate a lower layer containing theoligomer. After repeating the purification step once more, the oilylayer is evaporated in vacuo and the residue dried in a vacuum oven (50°C) over P₂ O₅. The average molecular weight of the product is determinedby Vapor Phase Osmometry. Using the above procedure the followingoligomeric polyacrylic acids end-capped with dodecyl mercaptan have beenprepared:

    ______________________________________                                        Amounts used, g./          Average                                            10g. acrylic acid          Molecular                                          Example Dodecyl Mercaptan                                                                           AIBN    Yield(g.)                                                                            Weight                                   ______________________________________                                        VII     3.0           2.0     6.0    1113                                     VIII    0.5           0.75    5.7    2250                                     IX      0.25          0.75    5.8    2520                                     X       0.10          0.75    6.3    2230                                     ______________________________________                                    

The sodium salts of the above oligometric polyacrylic acids are readilyprepared by dissolving the oligomer in water and neutralizing to pH 8.6with dilute sodium hydroxide. The resulting solution is then evaporatedto dryness to recover the solid sodium salt.

EXAMPLES XI - XXIV

Detergent formulations were prepared utilizing 50 weight percent of thesodium salts of the above prepared polyacrylic acids in combination with18 weight percent LAS, an anionic surfactant which is sodium linearsecondary alkyl (d₁₀ -C₁₅) benzene sulfonate, 10 weight percent of RUsilicate solids, a sodium silicate having an SiO₂ :N₂ O ratio of 2.4:1and 22 weight percent water. A control formulation was prepared, forpurposes of comparison, of 18 weight percent LAS, 50 weight percent ofpentasodium tripolyphosphate as the builder, 10 weight percent RUsilicate solids and 22 weight percent water.

Detergent building properties were measured with a Terg-O-Tometer testusing a 65% Dacron-35% cotton cloth soiled with vacuum cleaner dust. Thewash solution contained 180 ppm, 2:1 Ca++/Mg++, had an initial pH of 10,adjusted with dilute sodium hydroxide, and was maintained at atemperature of 120° F. Test concentrations of detergent formulations inthe wash solution were 0.1 and 0.2 percent. The average detergency units(DU) of the formulations is the final reflectance of the washed clothminus the initial reflectance of the soiled cloth (the average of tworuns), the reflectance being measured on a Gardner automatic colordifference meter, Model AC-3. Table I summerizes the results:

                                      TABLE I                                     __________________________________________________________________________                                 Detergency Units (DU)                                                                       % Efficiency                            Preparation                                                                         Average Molecular                                                                       Formulation                                                                           Experimental                                                                         Control                                                                              Experimental DU × 100        Example                                                                            Example                                                                             Weight    Concentration                                                                         Formulation                                                                          Formulation                                                                          Control DU                         __________________________________________________________________________    XI   I     10,270    0.1     25.5   25.5   100                                XII  I     10,270    0.2     28.7   29.0   99                                 XIII II     3,000    0.1     24.2   25.3   95                                 XIV  II     3,000    0.2     26.5   27.4   97                                 XV   III    2,000    0.1     22.8   24.1   95                                 XVI  III    2,000    0.2     26.7   26.6   100                                XVII IV     1,050    0.1     19.5   27.1   72                                 XVIII                                                                              IV     1,050    0.2     28.7   29.1   98                                 XIX  VII    1,113    0.1     25.5   26.7   96                                 XX   VII    1,113    0.2     28.3   29.3   97                                 XXI  VIII   2,250    0.1     24.9   26.7   93                                 XXII VIII   2,250    0.2     27.4   29.3   94                                 XXIII                                                                              IX     2,520    0.1     25.1   26.7   94                                 XXIV IX     2,520    0.2     28.0   29.3   96                                 __________________________________________________________________________

As can be seen from the data of Table I, the oligomeric polyacrylatebuilt detergents according to the present invention compare quitefavorably with the phosphate built detergent control. The test resultsclearly show that within the most preferred range of the presentinvention, i.e., an average molecular weight of between about 500 and3000, thiol end-capped polyacrylate can be successfully used as aphosphate replacement at both the 0.1 and 0.2 percent wash solutionconcentrations; hydroxy end-capped polyacrylate also performs very wellat the 0.1 and 0.2 percent concentrations at average molecular weight of2000 and 3000 but begins to show signs of strain at the 0.1 percentconcentration for the 1050 molecular weight. Note should be taken,however, that the 0.2 percent concentration of 1050 molecular weightpolyacrylate built detergent resulted in 98 percent efficiency which canbe considered as excellent. Further testing with the very low molecularweight 1050 builders of the present invention at 0.1 percentconcentrations determined that when the presence of the anionicsurfactant was boosted from 18 to 36 percent, the amount of builder andRU silicate remaining constant, the efficiency increased to a veryacceptable 93 percent.

Table II summarizes results obtained at formulation concentrations inwash solution of 0.15 percent with various detergent compositions. Inall cases the sodium salt of the polyacrylic acid was used and the sameTerg-O-Tometer conditions of test material and hardness, temperature andpH as in the above examples, were observed. STPP is pentasodiumtripolyphosphate; RU silicate solids is a sodium silicate having an SiO₂:Na₂ O ratio of 2.4:1; Tergitol 15-S-7 is an adduct of seven moles ofethylene oxide per mole of a random secondary alcohol derived fromC₁₁₋₁₅ normal parafins; C₁₄₋₁₆ HAMT is an ampholytic surfactant which issodium -N-2 hydroxy C₁₄₋₁₆ alkyl-N-methyltaurate; and, Sulfobetaine DCHis a zwitterionic surfactant which is cocodimethylsulfopropylbetaine.

                                      TABLE II                                    __________________________________________________________________________                      Examples XXV-XXXII, Percentages by Weight                                     XXV                                                                              XXVI                                                                              XXVII                                                                             XXVIII                                                                             XXIX                                                                              XXX                                                                              XXI                                                                              XXXII                             __________________________________________________________________________    1. Preparation Example VII                                                                      50 --  --  --   --  -- -- --                                2. Preparation Example VIII                                                                     -- --  50  --   --  -- -- --                                3. Preparation Example IX                                                                       -- --  --  --   50  -- -- --                                4. Preparation Example X                                                                        -- --  --  --   --  -- 50 --                                5. STPP           -- 50  --  50   --  50 -- 50                                6. RU Silicate Solids                                                                           10 10  10  10   10  10 10 10                                7. Sodium C.sub.15-18α-olefin                                                             18 18  --  --   --  -- -- --                                sulfonate                                                                     8. Tergitol 15-S-7                                                                              -- --  10  10   --  -- -- --                                9. C.sub.14-16 HAMT                                                                             -- --  --  --   18  18 -- --                                10. Sulfobetaine DCH                                                                            -- --  --  --   --  -- 18 18                                11. Water         ←                                                                           ←                                                                            ←                                                                            balance to 100%                                                                        →                                                                         →                                                                         →                          Detergency, DU's  24.5                                                                             27.4                                                                              27.7                                                                              28.8 26.7                                                                              28.4                                                                             29.0                                                                             29.9                              % Efficiency compared to                                                      control formulation (i.e.,                                                    XXV vs. XXVI, XXVII vs. XXVIII,                                                                 90     97       94     97                                   XXIX vs. XXX, XXXI vs. XXXII)                                                 __________________________________________________________________________

As can be seen from the data in Table II, particularly the comparisonsin the last line between the detergents built according to the presentinvention and the similarly constituted but phosphate built detergentcontrols, the efficiency is at least 90 percent and reaches as high as97 percent which can be considered as very favorable. Thus, at the 0.15percent wash concentrations, which is the level normally practiced inthis country, the detergents built according to the present inventionare adjudged to be excellent phosphate replacements.

Several of the oligomeric polyacrylates prepared in the above Examplewere than tested for biodegradability using either five day ortwenty-one day BOD testing. Table III shows this data as well aschemical oxygen demand (COD) and the BOD as a percentage of COD.

                                      TABLE III                                   __________________________________________________________________________                Molecular                                                                           Average       BOD as %                                      Preparation Example                                                                       Weight                                                                              BOD       COD of COD                                        __________________________________________________________________________    I           10,270                                                                              17  (5 Day)                                                                             1323                                                                              13                                            II          3,000 96  "     1432                                                                              22                                            III         2,000 103 "     1344                                                                              25                                            IV          1,050 139 "     1407                                                                              30                                            Acrysol A-1 <50,000                                                                             51  "     1340                                                                              13                                            VIII        1,113 229 (21 Day)                                                                            1488                                                                              54                                            Acrysol A-1 <50,000                                                                             65  "     1340                                                                              16.4                                          __________________________________________________________________________

BOD values are basis 300 mg. solids; COD values are basis 1000 mgsolids.

BOD as a % of COD is determined by ##EQU1##

The above figures clearly indicate that the novel polyacrylate oligomersof the present invention have noticeably improved biodegradability over5 days and excellent biodegradability over 21 days relative to thehigher molecular weight polymers. Careful note should be taken that theproduct of Preparation Example I having a molecular weight of 10,270 hada very poor biodegradability over five days and, in fact, would beclassified as non-degradable. For purposes of further comparison, acommercially available polyacrylate, Acrysol A-1 marketed by Rohm &Haas, having an average molecular weight of less than 50,000 was testedas above for five days and twenty-one days. The BOD as a percentage ofCOD for five days was between about 0 and about 13 percent and fortwenty-one days was 16.4 percent, which would also classify thismaterial as non-degradable.

Thus, it can be readily appreciated from each of the foregoing tablesthat this discovery of a novel class of polyacrylates which have bothhigh biodegradability and excellent detergent building propertiesanswers a long felt need in the art for a phosphorus free oligomericbuilder.

As this invention may be embodied in several forms without departingfrom the spirit or essential character thereof, the present embodimentsare illustrative and not restrictive. The scope of the invention isdefined by the appended claims rather than by the description precedingthem and all embodiments and formulations which fall within the meaningand range of equivalency of the claims are, therefore, intended to beembraced by those claims.

We claim:
 1. An oligomeric polyacrylate having an average molecularweight of greater than about 500 and less than about 10,000 and aformula represented by: ##STR2## wherein N is a whole number interger,R₁, and R₂ are moieties which do not impair biodegradability of themolecule and are selected from the group consisting of biodegradablehydroxy containing moieties, R₃ is selected from the group consisting ofhydrogen and alkyl groups having from one to six carbon atoms and M isselected from the group consisting of hydrogen, alkali metals, ammoniumand substituted ammonium cations.
 2. A compound as defined in claim 1wherein the repeating unit ##STR3## represents at least 45 mole percentof the molecule.
 3. A compound as defined in claim 1 wherein R₁ and R₂are selected from the group consisting of alkanols having from one tosix carbon atoms, glycols, glycol esters, glycolic acids, and salts ofglycolic acids.